Such nippers are used in endoscopic surgery, in particular in laparoscopy. The nippers shank formed by the tube is of substantial length, for instance 40 cm. Its outside diameter illustratively must be 4 mm in order to be insertable through corresponding endoscopic inlets into the patient. The rod used to drive the nippers must be of high mechanical strength in order to transmit high forces, including the tube which must be of a suitable wall thickness, ensuring that there can only be space inside the tube for the rod.
The nippers head bearing the nipper arms and the tube of such nippers should be freely rotatable relative to the grip, which typically is scissors-like, in order to allow seizure at arbitrary angular positions.
When the nipper arms are appropriately shaped, the nippers also may act as scissors.
The most significant feature of the nippers of this general type is disassembly into three parts. Following appropriate unlocking, the nippers head together with the rod, the tube together with is proximal fasteners and the terminal body with the grips, can then be taken apart. This feature is required for cleaning and sterilization.
The nippers comprise a nippers head which can be geometrically and axially interlocked at the distal shank end with a screw means or in particular with a bayonet lock. However, the rotational locking of the nippers head relative to the shank is problematical because of the torques acting on the nippers.
In German patent document C1 1 970 73 73, which shows a structure outside the species, this problem is solved by a spring-loaded bayonet lock which, however, involves substantial cleaning problems because of the exceedingly constricted conditions in the shank cross-section.
In European patent document B1 0,688,187 of the species, a bayonet lock of a more advantageous design but not secured against rotation is used. Non-rotatability of the nippers head is implemented at the distal tube end by resilient clamping elements which are inside this tube and which geometrically interlock with the rod when the tube is made to abut the end body.
A similar design is provided by the European patent document A1 0,633,002 wherein a leaf spring at the shank tube may be made to geometrically interlock with grooves in the rod and be secured in place in the operative position by means of the apposed end body.
These known designs of the species implement the axial displaceable non-rotatable interlock directly between tube and rod and consequently require complex designs of rod or tube. Problems in manufacture and cleaning therefore ensue.